This invention relates to enhanced oil recovery. More specifically, this invention relates to a process of enhancing oil recovery with a gas foam injection.
Many petroleum producing formations require assistance to economically produce hydrocarbons therefrom. The hydrocarbons can be recovered through the use of gas drives which are miscible with the in-place oil or generate a miscible drive of the in-place oil. Optionally, the gas drives may lower the viscosity of the hydrocarbons and enhance the flow of the hydrocarbons toward a production well. However, after initial breakthrough of the injected gas at the production well, the injected gas preferentially follows the path of the breakthrough. Thus, the total amount of the formation that is swept by the injected gas is limited. Solutions of commercial surfactants, such as Orvus K Liquid, a product of the Procter & Gamble Co., and Alipal CD-128, a product of the GAF Corporation, have been injected along with gas to create a gas foam flood. These materials are modified ammonium alkyl sulfates and ammonium salts of a sulfated linear primary alcohol ethoxylate, respectively. The surfactant and gas form a foam that inhibits the flow of the gas into that portion of the formation containing only residual oil saturation. Residual oil saturation is defined as the immobile oil remaining in that portion of the reservoir swept by gas or other enhanced recovery means. This forces the gas to drive the recoverable hydrocarbons from the less depleted portions of the reservoir toward the production well(s).
To maximize the extraction of hydrocarbons from a formation, it would be highly desirable to have foaming surfactants which inhibit the flow of gas in a gas zone containing only residual oil saturation. Furthermore, it would be desirable to have the surfactants in a gas foam recovery process which inhibit the flow of the gas in the zone which contains only the residual oil and enhance the flow of gas in the zone which contains the recoverable hydrocarbons. However, it is desirable not to have the flow of the recoverable hydrocarbons inhibited in the gas zone having an oil saturation greater than the residual oil saturation.